Summary of significant accounting policies - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Entity Incorporation Date Of Incorporation			Jan. 11, 1991
Concentration risk, customer			two customers each accounted for 10% or more of the Companys revenues	two customers each accounted for 10% or more of the Companys revenues
Aggregate percentage of revenue the from customers accounted for more than 10%			35.00%	28.00%
Deferred tax asset	$ 3,609,000		$ 3,609,000		$ 6,428,000
Operating loss carryforwards, limitations on use			Approximately $7,300,000 of the Companys $9,000,000 of NOLs are subject to annual limitations of $1,300,000
Options and warrants excluded from the calculation of diluted shares	75,000	80,843	75,000	80,843
Production and importation permission description			22 million pounds in 2015 and reduces by approximately 4.5 million pounds each year and ends at zero in 2020
Customer
Significant Accounting Policies [Line Items]
Accounts receivable, net	$ 2,309,000	$ 1,230,000	$ 2,309,000	$ 1,230,000